Biga: The day before making the bread, prepare the biga. In a medium bowl, sprinkle the yeast over the warm water and let stand until creamy, about 5 minutes. Whisk to dissolve the yeast. Add the room temperature water. Using a wooden spoon, stir in the flour, about 1 cup at a time. Stir for 3 to 4 minutes.

Transfer the Biga to a lightly oiled medium bowl. Cover tightly with plastic wrap. Let stand at cool (no higher than 78° F) room temperature for at least 6 hours and up to 24 hours. The Biga will triple in volume and may deflate; it will be wet and sticky. Refrigerate until ready to use, up to 5 days. (The Biga will get more sour as it ages. If the Biga is chilled, remove it from the refrigerator about 1½ hours before using. The Biga can also be frozen in an airtight container for up to 3 months. Defrost for 3 hours at room temperature before using.)

Dough: To make the dough, pour the warm water into the bowl of a heavy-duty stand mixer and sprinkle the yeast on top. Let stand until creamy, about 5 minutes. Add the room-temperature water and the measured amount of Biga. Attach the bowl to the mixer and fit with the paddle attachment. Mix on low speed until the water is chalky white and the Biga is broken into small pieces. Mix the flour, whole wheat flour, and salt. Gradually add enough of the flour mixture to the Biga mixture to form a dough. Switch to the dough hook. Knead on low speed until the dough is smooth and elastic, adding more flour or water to arrive at the proper consistency, about 7 minutes.

Turn the oven on for exactly 1 minute. Place the dough in the warm oven for 3 hours, or until the dough triples in volume. Carefully turn the dough onto a well-floured surface, taking care not to deflate the dough too much. Cut the dough into 2 equal portions. Working with one portion at a time, pull tight on the dough, rotating your hands around the edges until it forms a taut ball. Place in a well greased bread pan, rough side down. Repeat with the other portion.*

Turn the oven on for exactly 1 minute. Place the bread pans in the warm oven until dough had doubled in size, about one hour. Remove from oven.

Preheat oven to 450° F. Place a small iron skillet on bottom rack; heat. Pour about one-half inch of boiling water in pan. Place bread pans on top rack and bake until the loaves are golden brown and sound hollow when tapped on top, 35 to 45 minutes. Remove from oven, and turn bread out of pan onto wire racks. Cool completely. Yield: 2 loaves.

*NOTE: May make two dozen rolls rather than two loaves of bread. To make rolls, scale and make up dough into 2-ounce rolls. Proof until doubled in size. Brush top with cornstarch wash (3 Tablespoons water and 1 teaspoon cornstarch), or egg white wash (1 egg white and 1 Tablespoon water). Bake at 425° F 15-20 minutes or until golden brown.